There is a broad range of couplings for terminating, splicing or connecting various types of substrates such as coaxial cables and pipes. However, typical couplings have proven unsatisfactory for connecting and terminating such substrates which have rigid outer walls, e.g. rigid walled coaxial cables. As referred to herein, rigid walled coaxial cables means cables having an inner conductor and an outer jacket having the mechanical properties of being substantially inflexible, stiff or hard. An example of such a cable is a CATV cable which includes a center conductor surrounded by a foam dielectric and a rigid outer shielding jacket surrounding the foam dielectric. The shielding jacket is typically made from aluminum. While rigid, the aluminum jacket has the property of being malleable.
Such cables are generally exposed to the outdoor environment. It will be appreciated that the cables including their connections and terminations are exposed to all types of weather conditions. Such conditions may include temperature changes of 55.degree. C. or more within a twenty-four hour period. Additionally, the connections and terminations must be able to withstand water, ice, snow, extreme heat and cold and ultraviolet radiation, oxidation, pollution and salt spray.
Additionally, the tolerance limits for a given diameter cable may be quite broad. For example, cables of 0.500 inch diameter typically vary from 0.493 to 0.057. Thus, any suitable coupling must be able to accommodate such diameter differences.
One such coupling for such cables is a threaded coupling having two outer members which are threaded to one another and sealed by means of an O-ring. The coupling also includes two inside members, each having a tapered inside surface. The inside members grip the jacket deforming it to a smaller diameter such that a split ring between the inside members grips the jacket at the deformed portion. O-rings are used to seal the inside and outside members. An example of such mechanical compression connector or coupling is Blanchard U.S. Pat. No. 4,346,958.
Heat recoverable couplings for metallic tubings have previously been disclosed, for example in Hughes U.S. Pat. No. 4,135,743. Hughes discloses a coupling for metallic tubing comprising a hollow member fabricated from heat recoverable metal material and sized to recover upon heating to grip the tubing. The coupling may include a tapered portion with the wall thickness of each tapered portion decreasing away from the main body section.
Other couplings which include a heat recoverable metal driver member are described in Hill, U.S. Pat. No. 3,990,765. Hill discloses a connector for terminating the shielding of multiconductor cables. The Hill connector includes a grounding member (connector body) and a fastening means made from heat recoverable metal which is positioned inside the grounding member to grip and terminate flexible shielding braid.
Such heat recoverable metallic couplings have comparatively high compression strength and as disclosed in Hughes may include teeth which penetrate the surface of metallic tubing upon recovery. Such couplings have little transverse dimensional change, i.e. diametrical change upon recovery, generally recovery is in the range of two to five percent. Further such couplings are made from memory metal alloy including nickel titanium alloy and copper alloy. Such heat recoverable metal couplings may, upon recovery, have sufficient compression strength to cut through the rigid wall of a substrate of the type described herein. Where the wall of the substrate serves as an EMI shield, such a cut will encourage EMI leakage. Additionally, the relatively little transverse dimensional change of the heat recoverable metal couplings may prove to be unsatisfactory in accommodating the broad tolerance range of some substrates, particularly the commercially available coaxial cables described above.
Heat recoverable couplings made from polymeric material such as those disclosed in Booker, U.S. Pat. No. 3,320,355 have been disclosed for use in connecting or terminating flexible coaxial cable wires or shields, respectively. Booker discloses a sleeve of heat recoverable plastic material having a plurality of metallic clamp members disposed about the inner surface of the sleeve for receiving wires to be connected. The wires include a layer of soft dielectric. The connection is obtained by heating the sleeve and compressing the clamp members to penetrate the soft dielectric and thereby connect the wires. Booker discloses using heat shrinkable polyvinyl tubing. While the recovery force of the heat shrinkable polyvinyl sleeve may be sufficient to penetrate the soft dielectric of a cable, it would be insufficient to penetrate the surface of a rigid wall of a substrate, for example where the wall is made from aluminum or copper.